Finite element modeling and intravascular ultrasound elastography of vulnerable plaques: parameter variation

BACKGROUND AND GOAL: More than 60% of all myocardial infarction is caused by rupture of a vulnerable plaque. A vulnerable plaque can be described as a large, soft lipid pool covered by a thin fibrous cap. Plaque material composition, geometry, and inflammation caused by infiltration of macrophages are considered as major determinants for plaque rupture. For diagnostic purposes, these determinants may be obtained from elastograms (i.e. radial strain images), which are derived from intravascular ultrasound (IVUS) measurements. IVUS elastograms, however, cannot be interpreted directly as tissue component images, because radial strain depends upon plaque geometry, plaque material properties, and used catheter position. To understand and quantify the influence of these parameters upon measured IVUS elastograms, they were varied in a finite element model (FEM) that simulates IVUS elastograms of vulnerable plaques. MATERIALS AND METHODS: IVUS elastography measurements were performed on a vessel mimicking phantom, with a soft plaque embedded in a hard wall, and an atherosclerotic human coronary artery containing a vulnerable plaque. Next, FEMs were created to simulate IVUS elastograms of the same objects. In these FEMs the following parameters were varied: Young's modulus (E), Poisson's ratio (nu) in range 0.49-0.4999, catheter position (translation of 0.8 mm), and cap thickness (t) in range 50-350 microm. Hereby the resulting peak radial strain (PRS) was determined and visualized. RESULTS: Measured static E for phantom was 4.2 kPa for plaque and 16.8 kPa for wall.Variation of E-wall in range 8.4-33.2 kPa and/or E-plaque in range 2.1-8.4 kPa using the phantom FEM, gave a PRS variation of 1.6%, i.e. from 1.7% up to almost 3.3%; for variation in nu this was only 0.07%, i.e. from 2.37% up to 2.44%. Variation of E-lipid in range 6.25-400 kPa and E-cap in range 700-2300 kPa using the artery FEM, gave a PRS variation of 3.1%, i.e. from 0.6% up to 3.7%. The PRS was higher for lower E-lipid and E-cap; it was located at a shoulder of the lipid pool. Variation of nu gave only a variation of 0.17%. Variation of t and E-cap resulted in a PRS variation of 1.4%, i.e. from 0.3% up to 1.7%; thinner and weaker caps gave higher PRS. Catheter position variation changed radial strain value. CONCLUSIONS: Measured IVUS elastograms of vulnerable plaques depend highly upon the Young's modulus of lipid and cap, but not upon the Poisson's ratio. Different catheter positions result in different IVUS elastograms, but the diagnostically important high strain regions at the lipid shoulders are often still detectable. PRS increases when cap weakens or cap thickness decreases.     

Simultaneous57Fe and119Sn Mössbauer spectroscopy studies of a silica-supported FeSn catalyst

An iron-tin catalyst has been prepared by impregnation of a silica-support with a solution of organic salts of the metals in chloroform followed by reduction in hydrogen. Using a combined⁵⁷Co and Ba¹¹⁹SnO₃ source, the catalyst was studied simultaneously with both iron and tin Mössbauer spectroscopy. Reduction at 848 K of a catalyst prepared with an Fe∶Sn ratio equal to 1∶1 resulted in the formation of ordered FeSn alloy particles with an average diameter of about 20 nm. The particles were not affected by high-temperature treatment in an H₂/CO gas mixture.     

Nitrate reduction in clayey till by Fe(II) in clay minerals

In an area dominated by clayey till the distribution of nitrate and the Fe(II)/Fe(III) ratio have been measured below arable land till a depth of 20 metres. In the subsoil the nitrate (NO⁻ ₃) occurs in measurable quantities in the upper oxidised zone (until c. 3 m) and the Fe(II)/Fe(III) ratio is low. At the transition to the reduced zone the nitrate content decreases to below the detection limit and the Fe(II)/Fe(III) ratio is considerably increased. The results indicate that the Fe(II) in the clay minerals is oxidised by the nitrate which thereby is reduced.     

Formation and chemical stability of metallic glass particles prepared by thermolysis of Fe (CO)5

A ferrofluid has been prepared by thermal decomposition of Fe(CO)₅ in an organic liquid. Mössbauer spectroscopy and x-ray diffractometry studies show that the ferrofluid contains small particles of a metallic glass. The particles are only partly oxidized even after exposure of the ferrofluid to air at room temperature for 30 days.     

Stress concentration around holes in anisotropic sheets

The formulation of stress concentration problems of plane anisotropic elasticity in terms of integral equations is discussed. First the singular solutions of a concentrated force and a dislocation are formulated so that they remain valid in the case of double roots. The distribution of singularities on smooth curves is then treated, and general formulae for the stress discontinuities are given. Finally, the integral equations arising from stress boundary conditions are discussed, and the characteristics and numerical solution of one of the types are treated in detail.     

Theoretische Untersuchungen zur Molekülstruktur und Spektroskopie von Benzopyrylium-Verbindungen: Vollständig-optimierte S0- und S1-Molekülgeometrien des 5,6-Dihydrobenzo[c]xanthylium-Ions und Einfluß der Strukturfixierung sowie Substitution auf sein elektronisches Spektralverhalten in Absorption und Fluoreszenz

Summary Completely-optimized S₀ and S₁ molecular geometries of 5,6-dihydrobenzo[c]xanthylium ion are presented. Using these structural results the influence of structural fixation and of substitution on its spectral behaviour in absorption and fluorescence is studied theoretically and compared with experimental data.